1. Field of the Invention
The present invention relates to a calcium silicate board and a method of manufacture therefor, and in particular a lightweight (i.e., bulk specific gravity of 1.0 or less) calcium silicate board and a method of manufacture therefor.
2. Description of the Prior Art
Conventionally, calcium silicate boards have been widely used as a building material, chiefly for interior trimmings, because they are light, exceptionally easy to work with and dimensionally stable, and they are nonflammable. The molding processes for calcium silicate boards include Hatschek sheet machine process, press molding, and single layer molding, and the calcium silicate boards are manufactured from a compact formed from a raw material slurry, containing calcareous material, siliceous material, and inorganic filler, generally by reacting and curing the compact with saturated water vapor in a pressure vessel.
However, when manufacturing lightweight calcium silicate boards, particularly using the Hatschek sheet machine process, the interlaminar bonding within the compact is weak before hydrothermal reaction and the water content is high. During hydrothermal reaction, this gives rise to thermal expansion of excess water and high vapor pressure, which in turn leads to problems of interlaminar peeling and bursting.
Some of the methods used to overcome these problems are pressing the compact after molding and then subjecting it to hydrothermal reaction, or using a turnbuckle to squeeze the compact during hydrothermal reaction, but employment of these methods increases the bulk specific gravity and also increases labor requirements.
Japanese Patent Laid-Open No. 6-287083 discloses a method of removing excess water, but this method cannot be commonly used because it requires a special container or a vapor heater.
In addition in Japanese Patent Application Nos. 6-323225 and 7-5013 the inventors of the present invention have proposed methods in which amorphous siliceous material or silicate material, which reacts well with the calcareous material, is used as part of the siliceous material, or a curing agent such as Portland cement or granulated blast furnace slag is added, but these methods use expensive materials and increase the bulk specific gravity.
Further, the inventors of the present invention have proposed production methods for lightweight calcium silicate boards in which the strength of the compact (green sheet) before hydrothermal reaction and the interlaminar strength thereof is increased without the addition of siliceous material or silicate material or of curing agents such as Portland cement or granulated blast furnace slag, by using hemihydrate gypsum (Japanese Patent Appln. No. 7-138040) or anhydrous gypsum (Japanese Patent Appln. No. 7-169951) and interlaminar peeling or bursting does not occur during hydrothermal reaction.
However, when hemihydrate gypsum is used as a curing agent hydration occurs extremely quickly if the hemihydrate gypsum is used in slurry form and it becomes necessary to add a setting retarder to the slurry. And when anhydrous gypsum is used as a curing agent it becomes necessary to add a curing accelerator to the slurry, but adding setting retarders and curing accelerators and controlling the amounts added has made the manufacturing process for calcium silicate boards complicated.